Signaling system



June 13, 1933. B G EJGRNSQN 1,914,103

SIGNALING SYSTEM Filed Oct. 2, 1931 BY 272M ATTORNEY I 35 phase.

Patented June 13, 1933' UNITEDTISTAOTES PATENT OFFICE I BJORN e.BJoRNsoN, OF BROOKLYN, Nmv' YORK, AssIeNOR To BELL TELEPHONELAEORATORIEs, INCORPORATED, OE NEwvoRR, N. Y.', A CORPORATION OENEW YORKApplication filed October 2,1931. Serial No. 566,390.

This invention relates to signal controlled switching circuits andparticularly to radio receivers. I

One of the Outstanding diificulties encountered in radio signaling,particularly when short waves are employed, is fading, that is,variations in the waves as received from the transmission medium. It hasbeen found that a number of receiving stations can be so 10 located in arelatively small area that the signal fades difierently at each.Consequently, by continuously and automatically selecting between thesignal outputs of such stations so as always to supply to the signalcircuit the output of that station at which the wave fades least, it ispossible to greatly minimize the eifects of rapid changes and to reducethe possibility of the signal entirely fading out.

However, the waves received at a group of receiving stations asdescribed above will vary in phase as well as inamplitude and bothvariations appear to be quite at random. Consequently, when the phasevariations are such to produce at'the time of switching any materialdifference in phase between the output signal currents of the tworeceivers being switched, the result is to produce distortion in thesignal. This distor- 39 tion may be sufficient to seriously reduce theintelligibility particularly when the rate of switching is at all rapid.One Object of this invention is to reduce the distortion produced bysuch variations in In accordance with a specific preferred embodiment ofthis invention, a plurality of radio receivers are so arrangedgeographically that fading varies differently at each 40 and continuousand automatic control is provided to select that station the output ofwhich at any instant gives a useful signal. The signal channel leadingfrom each station is provided with two branches, by employing aswitching mechanism for reversing the polarity of each circuit. Thecontrol circuit disablesthe reversing mechanism in the channel inoperation and controls the reversing mechanism in the other channel orchannels so that at the time another channel is selected 7 phonereceiver 10. A switching circuit con- SIGNALING SYSTEM the phasedifference between the signal current in the channel being cut outandthat being cut in will not exceed Under ordinary conditionsofoperation, this circuit will permit switching from one channel toanother without any serious difficulty due to phase difference.

This invention is not limited to the specific embodiment described but,for example, may be employed in systems other than radio in which it isdesired to select between signal channels or, when more accurateadjustment is required, may be modified to include in each'channel aplurality of branches of small difference in phase shift. The inventioncan'be more readily understood by reference to the following detaileddescription in connection with the drawing which shows diagrammaticallyone embodiment of the invention in a radiotelephone receiver. There areprovided two radio receivers, and 200, the outputs of which are detectedin the detectors 101 and 201 respectively and supplied in common to thetele- 75 trols the two audio frequency paths so that the telephonereceiver 10 will always be responsive to the output of that one of thereceivers 100 or 200 which affords the best reception. r I v The controlcircuit comprises'the pushpull amplifiers 103 and 203 connected in theaudio frequency paths from the receivers 100 and 200 respectively andthe polarized relay 11 which controls the grid bias. of theseamplifiers. Ineach case the output of the receivers 100 and 200 isbranched off to amplifier-detectors 102 and 202 respectively.-The'amplifier-detectors 102 and 202 may be of' any of "the well knowntypes for amplify- QQ, ing and rectifying alternating current waves toproduce direct current of instantaneous amplitude determined by theamplitudeof the respective waves supplied thereto. Preferably they aremade selective to the carrier "5; frequency. The direct current Outputsof the amplifier-detectors 102 and 202 are supplied to the operatingwindings 104 and 204 respectively of the relay 11. The relay will beoperated by the current from that one of .9.

the receivers 100 or 200 having the larger output, to impress such anegative biasing potential upon the grids of the tubes of the amplifiers103 and 203 associated with the corresponding other receiver as to blockthat circuit for the transmission of audio frequency waves to thetelephone receiver 10. These biasing potentials are obtained from thebatteries 105 and 205 which are connected between the cathodes of theamplifiers 103 and 203 at the common ground connection 12 and theirgrids through the connections 108 and 208 respectively. Thus when therelay is in the position shown in the drawing, being operated by alarger current output from the receiver 200 than from the receiver 100,the battery 205 is short-circuited through the contact 209 and armatureof the relay, so that the amplifier 203 is rendered operative to permitthe transmission of the audio frequency output of the receiver 200 tothe telephone receiver- 10. On the other hand, the contact 109associated with the battery 105 is open so that the potential of thebattery 105 is im pressed between the cathodes and grids of the tubes ofthe amplifier 103, blocking those tubes to render inoperative the audiofrequency path from the receiver 100.

This control circuit is of the type disclosed and claimed in Patent1,470,954 to W. E. Beatty, October 16, 1923, in which the use of thepush-pull amplifiers eliminates disturbances due to the switchingoperation. Any

clicks produced due to the change of bias on the two tubes of thepush-pull amplifier are balanced out since the biasing potentials areimpressed in parallel on the two tubes, while the output circuits of theamplifier are only responsive to waves impressed in opposition upon thegrids.

However, imperfections in the balance between the two tubes of eitheramplifier may result in the effect that any such change in gridpotential such as that produced by switching operations will cause aclick in the output. Consequently, resistance-condenser networks 107 and207 are provided in the biasing circuit for retarding any change in gridpotential.

In order to secure a definite and quick action of the relay 11 there areprovided auxiliary throwing windings 110 and 210. These windings are soconnected that the relay is biased in favor of the side on which itsarmature rests. Thus with the relay in the position shown in thedrawing, current is supplied from the battery 105 to the winding 210 tobias it in the position shown, while the winding 110 is short-circuitedthrough the contact 209 and armature of the relay. This preventsindecision in operation of the relay during periods in which there maybe a rapid and small variation in the relative level of the outputs ofthe two receivers since the carrier of the block receiver must exceedthat of the operating receiver by a certain amount dependent upon thevalue of the bias before the armature begins to move. These windingsalso have the effect of accelerating the movement of the armature since,as soon as the armature leaves the contact, the bias is removed.Further, due to the fact that when the armature makes contact on theother side the bias is thrown on, the tendency to chatter is reduced.

The circuit so far described is effective for selecting between theoutputs of the two radio receivers so that that one which afi'ords thebest reception will always be supplying signals to the telephonereceiver 10. Any changes in the transmission conditions, such as fading,which produce a change in the relative outputs of the two receivers willresult in a reselection. However, such changes may produce, in addition.to variations in the amplitude of the received signals, variations inthe relative phase thereof. If, at the time of switching the receiver 10from one receiver to the other, there is a material difference in thephase of the signal outputs of the two receivers there will result adisturbance in the telephone receiven In order to reduce suchdisturbances each of the signal channels isprovided with a phasecontrolling circuit which operates automatically to reduce the phasechange at the moment of switching.

For this purpose each of the channels is provided with transformer, 111and 211, respectively. Each of these transformers is provided with twoprimary windings wound to induce voltages of opposite polarities in thesecondary winding. The connection of the primary windings in the audiofrequency channel is controlled by the relays 114 and 214, respectively.

Only the control circuit of relay 114 will be described in detail, sincethe control of each relay is effected by a similar circuit.

The relay 11 i is operated by two diii'erential windings 120 and 130,connected in the output of two rectifiers 121 and 131 respec tively. Therectifier 121 is operated by current supplied from the transformer 122through the amplifier 123. The rectifier 131 is similarly energized bycurrent supplied from the transformer 132 throu the amplilier 133. Thetransformer 122 is provided with one primary winding 12% which isconnected to the output of: detector 101, and a second primary winding125 which is.connected to the secondary winding of the transformer 211.These windings 124 and 125 are arranged to induce" aiding electromotiveforces in the secondary winding.

The transformer 132 is similarly provided with two primary windings 13 1and 135, connected respectively. to the output of the detector 101 andto the secondary. winding of the transformer 211. However, in this casethe windings 134 and 135 are so arranged as to induce opposingelectromotive forces in the secondary winding of the transformer.

Thus it will be that the relay 114 is controlled y the differencehot-ween two cur-v rents, one depending upon the sum of the.

the pull on the armature'will be proportional to the sine where or isthe phase difference between the two currents. will be seen that whenthe phase difference is 90, the pull on the armature is Zero butotherwise the pull will he directed to make the phase difference betweenthe currents in the outputs ofthe transformers 111 and 211 less than 90.The correction is effected by switching between the priassociated withthe receiver not in operation will le the only pair operated. Thus,under the conditions indicated in the drawing in which only the receiver200 is supplying signals to the telephone receivers 10, the am pl'fier108 being blocked by the action of the relay 11, the rectifiers 221 and231 are in active. Under his condition the rectifiers 121 and 131control the relay 11 1 so that the difference in the phase the currentsin the secondary windings of the transformers 111 and 211 will always beless than 90. During the moment of switchingfrom one of the receivers(200) to the other (100) the armature of the relay 11 is off both of thecontacts 109 and 209 so that both pairs of rectifiers 121 and 131, 221and 231, are inactive and the relay 114 will remain in the lastpositionpreventing any disturbance due toa phase correction during theinstance of switching from one receiver to the other.

What is claimed is: p

1. In a signaling system subject to variable transmission conditions, aplurality of receivers each receiving the same signal and so related toeach other that the received signals vary difierently at the severalreceivers with variations in transmission conditions, a receivingcircuit, means associated with said circuit to select from saidreceivers one whose signal output conforms to a desired require ment,and means effective at the instant of selection for automaticallycontrolling the phase of the signal supplied from the selected receiverto said circuit to prevent phase differences between the signalssupplied from said receivers from causing disturbances in said circuit.7

2. In a radio signaling system, a plurality of receivers receiving thesame signal and so related to each other that the received signals varydifferently at the several receivers with variations in transmissionconditions, a signal circuit, means for. continuously and automaticallyselectively connecting to said circuit that one of said receivers havinga signal output conforming to a preassigned requirement, a group ofpaths of different phase characteristics for each of said receivers,means for selectively connecting any path of each of said groups betweenthe corresponding receiver and said receiving circuit, means forrendering inoperative the path selecting means for that receiver whichat any instantis supplying signals to said circuit, and means forcontrolling the path selecting means in another receiver so that at anytime ofchanging from one receiver to said other receiver the phasedifference between the currents of said one and'said other receiverswill be a minimum. 7

3. In a radio signaling system, a plurality of receivers each receivinga wave representing the same carrier modulated by the same signal bandand so related to each other that the received waves vary differently atthe several receivers with variations in transmission conditions, asignal frequency circuit, means for continuously and automati-' callyselectively connecting to said signal frequency circuit that one of saidreceivers having a signal output conforming toa preassigned requirement,polarity reversing means for each receiver, means controlled by theselectively connecting means for rendering inoperative the polarityreversing v means of that receiver which at any instant is supplyingsignals to the signal frequency circuit, and means for controllingthepolarity reversing means in the other receivers so that at any timeof changing from one receiver to another the polarity of the outputcurrent from said other receiver will be such as to give the minimumphase difference between said output current and the output current fromsaid one receiver; f

4. In a signaling system, subject to variable transmission conditions, aplurality of receivers each receiving the same signal and so related toeach other that the received signals vary differently at the severalrecei ers with variations in transmission conditions, a signal circuit,means associated with said circuit for automatically and continuouslyselecting from said receivers one whose signal output conforms to adesired requirement, a plurality of transmission paths of differentphase characteristics connected between each of said receivers and saidselecting means, and means associated with each of said re ceiversforautomatically and continuously selecting that one of the respectiveplurality of transmission paths which will give a minimum phasedifference between the signal output of the path and the signal currentbeing supplied to the signal receiving circuit.

5. In a radio signaling system, a plurality of receivers receiving thesame signal and so related to each other that the received signals varydifferently at the several receivers with variations in transmissionconditions, a receiving circuit, means for continuously andautomatically selectively connecting to said receiving circuit that oneof said receivers having a signal output exceeding that of the other bya predetermined amount, polarity reversing means in the path from each.of said receivers to said receiving circuit, and means responsive to therelative phase of the waves received in said receivers for controllingsaid polarity reversing means to give a minimum phase difference betweenthe waves in the paths from said receivers.

6. In a signaling system subject to variable transmission conditions, afirst receiver, a second receiver, said receivers both receiving thesame signal and being so related to each other that the received signalsvary differently at each with variations in transmission conditions, asignal circuit, an automatic selecting circuit responsive to differencesin the signals received by said receivers, a first signal transmissionpath connecting said first receiver with said signal circuit, a secondsignal transmission path connecting said second receiver with saidsignal circuit, means controlled by said automatic selecting circuit foralternately blocking said transmission paths to select that receiver thesignal output of which meets a predetermined requirement, a group ofbranch paths of different phase shifts associated with each of saidplurality of the signal transmission paths, means responsive to therelative phases of the output of the corresponding receiver and of thesignal supplied to said signal circuit for selecting between the branchpaths of the corresponding group, and means responsive to said automaticselecting means for rendering inoperative that one of the branch pathselecting means associated with that one of said transmission paths overwhich signals are being transmitted to said signal circuit.

7. In a signaling system subject to variable transmission conditions, afirst receiver, a second receiver, said receivers both receiving thesame signal and being so related to each other that the received signalsvary differently at each with variations in transmission conditions, asignal circuit, an automatic selecting circuit responsive to differencesin the signals received by said receivers, a first signal transmissionpath connecting said first receiver with said signal circuit, a secondsignal transmission path connecting said second receiver with saidsignal circuit, means controlled by said automatic selecting circuit foralternately blocking said transmission paths to select that receiver thesignal output of which meets a pre determined requirement, phasereversal means in each of said transmission paths, and means forautomatically controlling the phase reversal means of the blockedtransmission path comprising means for comparing the sum and differenceof the current out put of the receiver associated with said blockedtransmission path and the current being supplied to said signal circuit.

8. In a signaling system subject to variable transmission conditions, afirst receiver, a second receiver, said receivers both receiving thesame signal and being so related to each other that the received signalsvary differently at each with variations in transmission conditions, asignal circuit, automatic selecting circuit responsive to differences inthe waves received by said receivers, a first signal transmission pathconnecting said first receiver with said signal circuit, a second signaltransmission path connecting said second receiver with said. signalcircuit, means controlled by said automatic selecting circuit foralternately blocking said transmission paths to select that receiver thesignal output of which meets a predetermined requirement, a first phasereversal means in said first transmission path, a second phase reversalmeans in said second transmission path, means tor controlling said firstphase reversal means in response to the difference between the sum anddifference of the signal output of said first receiver and the signaloutput oi said second transmission path, and means for controlling thesecond phase reversal means in response to the difterence between thesum and difference of the signal output of said second receiver and thesignal. output of said second transmission path.

9. lo a signaling system subject to variable transmission conditions, afirst receiver, a second receiver, said receivers both receiving thesame signal and being so related to each other that the received signalsvary ditferently at each with variations in transmis s n cond i ons, asignal circuit, an automatic selecting circuit responsive to differencesin the waves received by said receivers, a first signal tru Jsmissionpath connecting said first receiver -nth said signal circuit, a second sgnal smission path connecting said second recen r with said signalcircult, means controlled by said automatic selecting circuit forselectively blocking said transmission paths to select that receiver thesignal output of which meets a predetermined requirement,

a phase reversalmeans in said first'transmission path, a second phasereversal means in said second transmission path, means for producing arectified current proportional to the sum or" the signal output of saidfirst receiver and the signal output of said second transmission path,means for producing a rectified current proportional to the difierencein the signal output of said first receiver and the signal output ofsaid second transmission path, relay means responsive to the differencein said rectified currents for controlling said first phase reversalmeans, means for producing a rectified current proportional to the sumof the signal output of said second receiver and the signal output ofsaid first transmissi on path, means for producing a rectified currentproportional to the difference in the signal output of said receiver andthe signal output of said first transmission path, and relay meansresponsive to the difierence in the last mentioned rectified currentsfor con trolling said second phase reversal means.

10. In a signaling system according to claim 9, means responsive to theoperation of said automatic selecting means to block said firsttransmission path for rendering inoperative the first two mentionedmeans for pro ducing rectified current, and means responsive to theoperation of said automatic selecting means to block said secondtransmission path for rendering inoperative the last two mentionedrectified current producing means.

11. In a transmission system, two'sources of current of varying phase, atransmission path associated with each source, and means for reducingthe phase difference between the current output of said transmissionpaths comprising a phase reversal means in one of said transmissionpaths, and means for controlling said phase reversal means in responseto the sum and difference of the current-from the respective one of saidsources and the current output of the other transmission path.

In witness whereof, I hereunto subscribe my name this 29th day ofSeptember, 1931.

BJORN G. BJoRNsoN.

